The measuring of concentration of materials and a subsequent regulation of the concentration to a required value is an important operation for all kinds of chemical manufacture. The ultrasonic measuring device possesses properties which adapt it for application in automatic regulating circuits as a pick-up device. The probe of the apparatus can be situated directly in the investigated liquid. It requires no attendance and operates automatically by the impulse method with a high repeating frequency so that it yields practically continuous information about conditions of the investigated medium. The dependence of the speed of propagation of ultrasonic waves in the liquid on its composition-on its concentration is thereby utilized for measurements. The dependence of the speed of propagation on temperature is linear for most liquids up to critical temperatures.
Two main types of temperature dependent ultrasonic propagation variations for different concentrations of some material are known. The first type of dependence on temperature for a certain concentration of the investigated material is the simpler of these, as the individual straight lines of a resulting graph are parallel as, for instance, for aqueous solutions of H.sub.2 SO.sub.4, NaOH, glycerol and others. The line slopes for the second type of dependence are different for each concentration of a certain solution. The temperature dependence usually changes its sign within a relatively narrow extent of concentration, for instance, with nitric acid 20-30%, ammonia, water, and others.
The compensation of the influence of temperature on solutions having the first type of dependence is accomplished in different ways. There are known methods based on measurements of temperature and on introduction of corrections to the output signal which are proportional to variations of temperature. Another method utilizes, for the determination of the concentration of the solution, a reference solution maintained at the same temperature as the measured solution. The difference of time intervals corresponding to the difference of the speed of sound propagation in both solutions is constant with variations of temperature, and changes only in case of a change of concentration.
These methods, however, cannot be applied for measuring the concentration of solutions of the second type of dependence due to variation of the line slope.